The importance of the mouse for biomedical research cannot be overstated. Genetic investigations of mouse mutations were initiated at the turn of the century, shortly after the rediscovery of Mendel's laws. More recently, the development of technologies to manipulate the mouse germ line by transgenesis or homologous recombination has made the mouse the definitive system for the study of mammalian gene function. With the rapid progress in the characterization of the mouse genome, and the application of efficient methods of mutagenesis such as ENU treatment or gene trapping, potential for further progress is unparalleled. This is manifested in the stated aim of several consortia of investigators to generate large numbers of mutant mice. We propose an annual workshop to facilitate the interaction of researchers who have invested their research efforts in these various technologies. The aim will be to discuss progress, problems, new technologies, and logistical issues related to the distribution and utilization of these resources. This meeting will be the successor to a series of workshops that have emphasized several of the component technologies, such as ENU mutagenesis and gene-trap mutagenesis. Importantly, this forum will aim to include a wide variety of technologies, so that their potential advantages and disadvantages can be considered and discussed. This workshop will also aim to carry on the tradition of international representation that has been characteristic of the previous meetings. Ultimately, this workshop will serve the goal of improving public health by facilitating the generation and utilization of model systems for biomedical investigation.